Materials engineering at the nanometer scale can provide smaller devices than those currently available. In particular, research on semiconductor nanostructures with size-dependent optical and electronic properties, such as quantum-dots, one-dimensional quantum wire transistors and light emitting devices with extremely low power consumption is motivated by potential applications. Silicon is a material of great interest for nanostructures because of its important role in the field of microelectronics.
Since the 1960's, silicon whiskers grown by the vapor-liquid-solid (VLS) reaction have been extensively studied. After the VLS technique, many efforts have been made to further improve the synthesis of silicon nanowires by employing different techniques, such as photolithography technique combined with etching and scanning tunneling microscopy. These methods are tedious and normally produce only a limited number of strands of nanowires. Recently, silicon nanowires have been synthesized by laser ablation of metal-containing silicon targets (Wang, et al., Chemical Physics Letter, 283, p.368, 1998; Zhang et al., Applied Physics Letter, 72, p.1835, 1998; Morales et al., 279, p. 208, 1998). However, since metals were used as a catalyst, this method is in fact an extension of the VLS technique. The drawbacks of the VLS technique in producing nanowires are (1) contamination by the metal catalyst and (2) the extremely low yield of production, Therefore, one of the challenging issues in the field of silicon nanostructures has been the synthesis of high-quality, high purity silicon nanowires in large quantities.